The present disclosure relates to a drum unit having a photosensitive drum, and an image forming apparatus having same.
The drum unit including the photosensitive drum and a main body supporting the photosensitive drum is known. The photosensitive drum has a hollow cylindrical drum sleeve, and resin flanges press-fitted into both ends of the drum sleeve. The flanges each have a supporting portion protruding from a lateral face thereof in an axial direction. The drum unit main body has sliding bearing portions at locations corresponding to both axial ends of the photosensitive drum. The supporting portions are inserted into the sliding bearing portions, and the photosensitive drum is thereby attached to the drum unit main body. The photosensitive drum is rotationally driven with the supporting portions and the sliding bearing portions sliding on each other.
In the case of a supporting structure for the photosensitive drum in which, as described above, supporting portions protruding from flanges are directly supported by bearing portions, the resin flanges expand due to the heat generated by friction during the rotational driving. As a result, the supporting portions of the flanges and the bearing portions of the drum unit main body interfere with each other, sometimes causing rotation failure. For this reason, a clearance that takes into account thermal expansion is provided between the supporting portions of the flanges and the bearing portions of the drum unit main body. There has been proposed in the art the use of a resin material having a low linear expansion coefficient for the flanges, and the resin material is selected so that the rotational driving of the photosensitive drum is not affected by thermal expansion of the flanges.
However, in the above art, thermal expansion of the flanges is allowed within a predetermined range, and therefore when the environmental temperature changes, the clearance between the flanges and the bearing portions changes. This change in clearance is likely to affect the rotation accuracy of the photosensitive drum. In particular, in the case where the photosensitive drum rotates at a high speed, the expansion of the flanges due to friction is significant, and therefore a large clearance is provided.
When a large clearance is provided, the rotational driving force when the flanges are not thermally expanded is less likely to be transmitted accurately, the rotation accuracy of the photosensitive drum decreases, and the image quality of the image forming apparatus decreases. In addition, it is difficult to suppress the abrasion of the supporting portions caused by repeated rotation of the photosensitive drum only by selection of resin material. Therefore, the abrasion of the supporting portions may destabilize the drive transmission, and may cause further rotation failure.